The invention relates to telecommunication exchange installations, and particularly, the coupling point switching systems therein.
In rating the capacity of a telecommunication exchange system one must consider operational as well as economic points of view: on the one hand the exchange system must be so equipped that it can satisfy the burden of traffic while maintaining a prescribed quality in properly routing the traffic; on the other hand, the expense involved in the operation of the communication system should be as small as possible. Coupling systems are an essential component of telecommunication traffic systems. These arrangements of switching links have the function of connecting input lines with output lines, connections being chosen according to the routing desired. Every connection is formed through appropriate activation of one or more coupling point switches of a coupling system.
Coupling point switches of this sort are often arranged in a coupling system in the form of switching matrices, that is, in a configuration in which a specific input switching matrix row has access to a specific output switching matrix column over a (2 or 4 line) coupling point switch, which lies in the junction of the applicable switching matrix row and the applicable switching column. The size of the switching matrix used in a coupling system influences strongly the number of necessary coupling point switches and the extent of the holding information necessary for maintaining established connections. Theoretically, the task assigned to a coupling system with N/2 inputs and N/2 outputs demands, respectively, a combination of any N/2 different connections of a particular input with any particular output from a total of N/2 possible connection combinations, 2.multidot.(1dN/2) coupling point switches and a holding datum of T=(1dN/2).uparw. bits, where (1dN/2).uparw. denotes the next higher whole member after 1dN/2.
In practice, it is fundamentally the case that the larger the switching matrices of the coupling system are, the more coupling point switches are necessary, yet the less the extent of the necessary holding data is. Thus, for a single stage coupling system having N/2 input lines and N/2 output lines in the form of a quadratic coupling point matrix. (N/2).sup.2 coupling point switches are necessary with a holding data requirement of Q=N/2.multidot.(1dN/2).uparw. bits. This is a practical necessity. Although, for a multiple stage coupling system which is composed of minimal switching matrices with 2 inputs and 2 outputs, respectively, a sharp decline of the necessary number of coupling point switches with a simultaneous increase of the necessary extent of holding data is to be expected.
Under certain conditions, however, not only can a saving be made on coupling point switches with application of such minimal switching matrices, but at the same time, a saving is achievable with respect to the necessary extent of holding data. Thus, it is known (Bell System Technical Journal, Vol XLIII, July, 1964, #4, Part 2, pages 1641 to 1656; Bell System Technical Journal, Vol. XLVII, May-June 1968, #5, pages 813 to 822; German Pat. No. 1,922,891) to use a coupling system for connecting N/2 input lines with N/2 output lines, which has switching matrices (binary switching matrices) having two first lines and two second lines, of which one first line is connected with either of said second lines, and the other of said first lines with the other of said second lines. Thus, in the switching matrices there is always a through-connection between the two first lines and the two second lines, namely an "uncrossed" or a "crossed" through-connection. The switching matrices are interconnected in such a manner that, respectively, both second lines of a preceding switching matrix are connected, respectively, with a first line of two succeeding switching matrices, and the two first lines of a succeeding switching matrix are connected, respectively, with a second line of two preceding coupling multiples. In such known coupling systems the three middle coupling stages of the binary switching matrices are combined pairwise in such a way that each of the two binary switching matrices of a pair of binary coupling multiples of a preceeding coupling stage is connected with each of the two binary switching matrices of a corresponding pair of binary switching matrices of the succeeding coupling stage. In the remaining coupling stages the two lines of the nth binary switching matrix of the kth coupling stage are connected, respectively, with a first line of the (2n-1)th and of the 2nth binary switching matrix of the--looking at the three middle coupling stages--(k+1)th coupling stage (given 0&lt;n&gt;N/8), i.e., of the (2n-1-N/4)th and of the (2n-N/4)th binary switching matrix of the (k+1)th coupling stage (given N/8&lt;n.ltoreq.N/4). With such a centrally symmetric construction B=N/2.multidot.1dN/2-N/4 binary switching matrices are necessary, which are arranged in 2.multidot.1dN/2-1 stages (of differential configuration) to N/4 binary switching matrices, and with a range of holding data of likewise B bits; with unsymmetric so-called nested tree-type construction according to U.S. Pat. No. 3,593,295, and Bell System Technical Journal Vol. XLVII, May-June 1968, #5, pages 813 et seq., J=N/2.multidot.1dN/2-N/2+1 binary switching matrices and a holding data capacity of J bits are necessary.
These known coupling systems, which in any case are free of blocking under appropriate rearrangement of existing connections, enable, meanwhile, only connections between the N/2 inputs on the one hand and the N/2 outputs on the other hand, and are, therefore, only suited for traffic between two groups of connecting lines. In practice, one must also, however, deal many times with traffic between connecting lines of one and the same group, which means for the coupling system that the differentiation between inputs and outputs disappears and that all N connecting lines must be connectable pairwise with each other in arbitrary combinations.
It is an object of the invention to provide a means to achieve a coupling system constructed only of binary switching matrices which satisfies these conditions.